Problem with package managers are they are quite expensive to run, so hard to manage in an otherwise open source ecosystem. There was some controversy around NPM before the GitHub acquisition https://www.businessinsider.com/npm-cofounder-laurie-voss-re..., which I guess is the exact problem a non-profit such as RubyCentral tried to solve.
I would GitHub would be quite well-positioned to set up infrastructure around a fork of RubyGems if things fall apart.